1. Field of the Invention
The present invention relates to a drive power control method and apparatus for a solid state light source. More particularly, the present invention relates to a drive power control method and apparatus in a light source application that requires high luminance sequential color light, such as a single-digital light processor (DLP) projection display.
2. Description of the Related Art
In conventional applications that require high luminance light sources, such as projection display systems or stage lighting, gas discharge lamps such as ultra high performance (UHP) lamps are usually used. However, gas discharge lamps suffer from short lifetimes and cause environment pollution.
In more detail, FIG. 1 is a schematic view of a conventional single-DLP projection system. A UHP lamp 201 generates a white light which is collected by a reflector 202 and condensed by a lens 203. A color wheel 204 allows primary colors such as red (R), green (G) and blue (B) light to pass through sequentially (see FIG. 3 and more detailed descriptions below). The different color light sequentially arrives at a spatial light modulator 210 through a series of optics such as integration rod 205, lenses 206, 207 and 208, and TIR prism 209. The modulated color light is directed to a projection lens 211 and forms an image on a screen.
A more environmentally-friendly choice of light source for this type of application is solid state light (SSL) sources based on laser diodes (LDs) or light emitting diodes (LEDs). One solution of replacing UHP lamps by a SSL source is shown in FIG. 2. A UV or blue SSL source 111 generates a UV or blue light which excites a wavelength conversion material such as a phosphor carried on a wheel 112 to generate a wide spectrum light that has more than one primary color light needed for projection display. For example, the phosphor on the wheel 112 may be a yellow phosphor such as a YAG:Ce phosphor. Since the yellow phosphor's emission light contains both green and red components, a green color and a red color can be generated by placing color filters downstream of the phosphor. A second light source 116 is provided, which may be blue LDs or LEDs. The phosphor's emission light from the wheel 112 and the blue light from the second light source 116 are combined by a combining device (e.g. dichroic filter) 114 to generate a white light, which has all three primary color components (red, green and blue) needed for projection display. This white light is directed by a lens 115 to a color wheel 204. The color wheel 204 has several filter segments that filters the white light into primary color lights. Therefore, the SSL source system, formed by the first SSL source 111, the phosphor wheel 112, optics (e.g. lens) 113, the light combining device (e.g. dichroic filter) 114, optics (e.g. lens) 115 and the second SSL source 116 shown in FIG. 2, can replace the UHP lamp 201 in FIG. 1, while other components of the system shown in FIG. 2, including the color wheel 204 and optical components downstream of it, can remain unchanged.
FIG. 3 shows the schematic structure of a color wheel 204 used in the system shown in FIGS. 1 and 2. In this example, the color wheel 204 includes three color filter segments which transmit red, green and blue light, respectively, and block other lights. When the color wheel 204 is driven by a drive mechanism to rotate, the color filter segments are sequentially moved into the light path of the optics 203/115 and illuminated by the white light, and red, green and blue lights passes through the color wheel sequentially. Referring to FIG. 5A as an example, the output light from the color wheel 204 has a repeating sequence shown over two periods of the color wheel's rotation.